1. Field of the Invention
The present invention relates to an improvement of a hard film for wear resistant applications such as plastic working tools (e.g., punching and forming dies) and cutting tools (e.g., tips, drills and end mills), a process for forming said hard film, and a target used as an evaporating source to form said hard film.
2. Description of the Related Art
In the past, for the purpose of improving wear resistance of cutting tools using cemented carbide, cermet or high-speed tool steel as base material, it has been practiced to perform coating of hard film such as TiN, TiCN, TiAlN, etc. In particular, compound nitride film of Ti and Al (hereinafter referred as xe2x80x9cTiAlNxe2x80x9d) exhibits excellent wear resistance, and it is applied on cutting tools for high-speed cutting operation or for cutting the material with high hardness such as hardened steel instead of the film, which comprises nitride, carbide or carbide-nitride of titanium. Further, more recently, in addition to two-element material such as TiAlN, attempts have been made to improve the characteristics by adding a third element. For instance, in the Japanese Patent Publications Laid-Open 3-120354, 10-18024, 10-237628, and 10-305935, it is disclosed that TiAlVN or (TiAlV)(CN) film added with V exhibits superb cutting characteristics in the cutting operation of the material with low hardness such as S50C. However, it is difficult to say that these films have good cutting characteristics to the materials with high hardness such as hardened steels. To cope with the increasing trend directed toward high cutting speed, there are now strong demands to have the film with higher wear resistant property.
To solve the above problems, it is an object of the present invention to provide a hard film for wear resistant applications such as cutting tools, which is suitable for cutting at high speed and with higher efficiency and which has higher hardness and better wear resistance than TiAlN or (TiAlV)(CN) used in the past. The object of the invention is also to provide a method for forming such hard film, and further to provide a target for efficiently forming the hard film for wear resistant applications such as cutting tools of the present invention.
To attain the above object, the present invention provides a hard wear resistant film composed of (Alb,[Cr1xe2x88x92xcex1Vxcex1]c)(C1xe2x88x92dNd), and the composition of the components satisfies the conditions:
0.5xe2x89xa6bxe2x89xa60.8,
0.2xe2x89xa6cxe2x89xa60.5,
b+c=1,
0.05xe2x89xa6xcex1xe2x89xa60.95,
0.5xe2x89xa6dxe2x89xa61
(where b and c each represents atomic ratio of Al and Cr+V, d denotes atomic ratio of N, and xcex1 represents atomic ratio of V). (Hereinafter, this film may called xe2x80x9cthe first filmxe2x80x9d.)
Further, the present invention provides a hard wear resistant film composed of (Ma,Alb,[Cr1xe2x88x92xcex1Vxcex1]c)(C1xe2x88x92dNd), where M is at least one element selected from Ti, Nb, W, Ta and Mo, and said hard film satisfying the conditions:
0.02xe2x89xa6axe2x89xa60.3,
0.5xe2x89xa6bxe2x89xa60.8,
0.05xe2x89xa6c,
a+b+c=1,
0.5xe2x89xa6dxe2x89xa61,
0xe2x89xa6xcex1xe2x89xa61
(where a, b and c each represents atomic ratio of M, Al, and Cr+V, d denotes atomic ratio of N, and xcex1 represents atomic ratio of V). For the case where M is Ti and the value of xcex1 is 0 in the preferred aspect of the invention, it has been already applied as the Japanese Patent Application 2001-185464 (not yet laid-open), and this is exempted from the present invention. (Hereinafter, this film may be called the second hard film.) Further, when the value of xcex1 is 1, it is preferable that the values of b and c satisfy the conditions:
0.5xe2x89xa6bxe2x89xa60.8,
0.05xe2x89xa6c,
0.7xe2x89xa6b+c.
Also, in the hard wear resistant film according to a preferred aspect of the present invention, the value of d is 1, and crystal structure has rock salt structure as main structure. Also, it is preferable that, when diffraction line intensities of (111) plane, (200) plane and (220) plane of rock salt structure measured by X-ray diffraction based on xcex8xe2x88x922xcex8 method are set to I(111), I(200) and I(220) respectively, these values satisfy the expressions (1) and/or (2) and the expression 3 given below:
I(220)xe2x89xa6I(111)xe2x80x83xe2x80x83(1)
I(220)xe2x89xa6I(200)xe2x80x83xe2x80x83(2)
I(200)/I(111)xe2x89xa70.3xe2x80x83xe2x80x83(3)
The hard wear resistant film of the present invention include: a hard film satisfying the above requirements and two layers or more of hard films different from each other and laminated on each other; or one layer or two layers or more of the hard films of the present invention have crystal structure with rock salt structure as main structure and are attached on one surface or both surfaces of the hard film, and one layer or more of metal layers or alloy layers containing at least one element selected from 4A Group, 5A Group, 6A Group, Al and Si are laminated; at least one layer selected from metal nitride layer, metal carbide layer and metal carbide-nitride layer having different composition as that of the hard film as described above are laminated.
The present invention also defines a method for forming the hard wear resistant film as described above. It is a method for forming the film defined in the present invention on an object to be processed by evaporating and ionizing metal in an atmosphere of film-forming gas and for forming the film while promoting conversion of the film-forming gas together with the metal into plasma. The present invention also provides the hard film using arc ion plating method (AIP method) by evaporating and ionizing the metals, which constitute the target, by arc discharge, and forming the film defined in the present invention on an object to be processed, whereby a line of magnetic force is formed, which runs almost in parallel to the normal to the evaporating surface of the target and running in parallel to or slightly divergent from the normal to the evaporating surface of the target, and the film is formed by promoting conversion of the film-forming gas near the object to be processed to plasma. In this case, it is preferable that bias potential applied on the object to be processed is set to the range of xe2x88x9250 V to xe2x88x92300 V with respect to the earth potential. Also, it is desirable that the temperature of the object to be processed (may be referred as substrate temperature hereinafter) during film-forming operation is set to the range of 300xc2x0 C. to 800xc2x0 C. It is also preferable that partial pressure or total pressure of the reactive gas during film-forming operation is set to the range of 0.5 Pa to 6 Pa.
The reactive gas in the present invention is a gas such as nitrogen gas, methane gas, ethylene gas, acetylene gas, etc. and contains elements required for the compositions of the film. Other types of gas, i.e. rare gas such as argon gas, is called xe2x80x9cassist gasxe2x80x9d. These are called together as xe2x80x9cfilm-forming gasxe2x80x9d.
Further, the present invention also includes a target for forming a hard film, which comprises Al, Cr and V, or M (where M is at least one element selected from Ti, Nb, W, Ta and Mo), Al, Cr, and/or V, and which has relative density of 95% or more. It is preferable that size of each of the voids present in the target is not smaller than 0.3 mm in radius.
For forming the hard film (the first hard film) of the present invention expressed by (Alb,[Cr1xe2x88x92xcex1Vxcex1]c)(C1xe2x88x92dNd) it is preferable to use a target, which comprises (Aly,[Cr1xe2x88x92xcex2Vxcex2]z) and satisfying the conditions:
0.5xe2x89xa6yxe2x89xa60.8,
0.2xe2x89xa6zxe2x89xa60.5,
y+z=1,
0.05xe2x89xa6xcex2xe2x89xa60.95
(where y and z each represents atomic ratio of A and Cr+V, and xcex2 denotes atomic ratio of V).
Also, for forming the hard film (the second hard film) of the present invention expressed by (Ma,Alb,[Cr1xe2x88x92xcex1Vxcex1]c)(C1xe2x88x92dNd), it is preferable to use a target, which comprises (Mx,Aly,[Cr1xe2x88x92xcex2Vxcex2]z), where M is at least one element selected from Ti, Nb, W, Ta and Mo and satisfying the conditions:
0.02xe2x89xa6xxe2x89xa60.3,
0.5xe2x89xa6yxe2x89xa60.8,
0.05xe2x89xa6z,
x+y+z=1,
0xe2x89xa6xcex2xe2x89xa61
(where x, y and z each represents atomic ratio of M, Al, and Cr+V, and xcex2 denotes atomic ratio of V). For forming the hard film of the preferred aspect of the present invention where M is Ti, it is preferable to use a target, in which M is Ti. However, in the hard film of the present invention, the case where M is Ti and the value of xcex1 is 0 is exempted. Therefore, for the target also, the case where M is Ti and the value of xcex2 is 0 is exempted.
Further, for forming the hard film, in which M is Ti and the value of xcex1 is 1 and the value of atomic ratio (b+c) of Al+V is 0.7 or more, the value of b is within the range of 0.5 to 0.8, and the value of c is more than 0.05, it is preferable to use a target, in which the value of y and z is 0.5 less than yxe2x89xa60.8, 0.05 less than z, 0.7xe2x89xa6y+z, and xcex2=1.
In the target as described above, it is preferable that oxygen content in the target is 0.3 mass % or less, hydrogen content is 0.05 mass % or less, and chlorine content is 0.2 mass % or less. Further, it is preferable that Cu content is 0.05 mass % or less, and Mg content is 0.03 mass % or less.
Other and further objects, features and advantages of the invention will appear more fully from the following description.